contrib/valyala/fasthttp.v1: fix memory leak of spanOpts

[0angelic0]

What does this PR do?

This PR fixes the memory leak of contrib/valyala/fasthttp.v1 WrapHandler function by moving the initialization of spanOpts to be in the closure anonymous function that will return as a fasthttp.RequestHandler instead of WrapHandler function. So it will be garbage collected every time the request handler end.

Motivation

Fixes #2961

Reviewer's Checklist

• Changed code has unit tests for its functionality at or near 100% coverage.
• System-Tests covering this feature have been added and enabled with the va.b.c-dev version tag.
• There is a benchmark for any new code, or changes to existing code.
• If this interacts with the agent in a new way, a system test has been added.
• Add an appropriate team label so this PR gets put in the right place for the release notes.
• Non-trivial go.mod changes, e.g. adding new modules, are reviewed by @DataDog/dd-trace-go-guild.

[darccio]

@0angelic0 Thanks for contributing this fix. It'll released during this month.